Moustafa, E., S. Mohammed, S. Abdel-Wanis, T. Mahmoud, and E.-S. El-Kady. “Review Multi Pass Friction Stir Processing”. American Scientific Research Journal for Engineering, Technology, and Sciences, vol. 22, no. 1, July 2016, pp. 98-108, https://asrjetsjournal.org/index.php/American_Scientific_Journal/article/view/1891.